An operando spectroscopic investigation of the Re2O7.2H2O adduct obtained by controlled hydration of Re2O7.

We provide here a comprehensive investigation spectroscopic of the controlled hydration of Re2O7 using Raman, FTIR and XAS techniques in complement with ab initio modelling for confirming the spectral assignments. Hence, the Raman signature of Re2O7.2H2O was obtained, and the evolution kinetics was investigated to provide a detailed description of the hydration process.

Hyperspectral full-field quick-EXAFS imaging at the ROCK beamline for monitoring micrometre-sized heterogeneity of functional materials under process conditions.

Full-field transmission X-ray microscopy has been recently implemented at the hard X-ray ROCK-SOLEIL quick-EXAFS beamline, adding micrometre spatial resolution to the second time resolution characterizing the beamline. Benefiting from a beam size versatility due to the beamline focusing optics, full-field hyperspectral XANES imaging has been successfully used at the Fe K-edge for monitoring the pressure-induced spin transition of a 150 µm × 150 µm Fe(o-phen)2(NCS)2 single crystal and the charge of millimetre-sized LiFePO4 battery electrodes. Hyperspectral imaging over 2000 eV has been reported for the simultaneous monitoring of Fe and Cu speciation changes during activation of a FeCu bimetallic catalyst along a millimetre-sized catalyst bed. Strategies of data acquisition and post-data analysis using Jupyter notebooks and multivariate data analysis are presented, and the gain obtained using full-field hyperspectral quick-EXAFS imaging for studies of functional materials under process conditions in comparison with macroscopic information obtained by non-spatially resolved quick-EXAFS techniques is discussed.

Insight into the Nature of the ZnO x Promoter during Methanol Synthesis.

Despite the great commercial relevance of zinc-promoted copper catalysts for methanol synthesis, the nature of the Cu-ZnO x synergy and the nature of the active Zn-based promoter species under industrially relevant conditions are still a topic of vivid debate. Detailed characterization of the chemical speciation of any promoter under high-pressure working conditions is challenging but specifically hampered by the large fraction of Zn spectator species bound to the oxidic catalyst support. We present the use of weakly interacting graphitic carbon supports as a tool to study the active speciation of the Zn promoter phase that is in close contact with the Cu nanoparticles using time-resolved X-ray absorption spectroscopy under working conditions. Without an oxidic support, much fewer Zn species need to be added for maximum catalyst activity. A 5-15 min exposure to 1 bar H2 at 543 K only slightly reduces the Zn(II), but exposure for several hours to 20 bar H2/CO and/or H2/CO/CO2 leads to an average Zn oxidation number of +(0.5-0.6), only slightly increasing to +0.8 in a 20 bar H2/CO2 feed. This means that most of the added Zn is in a zerovalent oxidation state during methanol synthesis conditions. The Zn average coordination number is 8, showing that this phase is not at the surface but surrounded by other metal atoms (whether Zn or Cu), and indicating that the Zn diffuses into the Cu nanoparticles under reaction conditions. The time scale of this process corresponds to that of the generally observed activation period for these catalysts. These results reveal the speciation of the relevant Zn promoter species under methanol synthesis conditions and, more generally, present the use of weakly interacting graphitic supports as an important strategy to avoid excessive spectator species, thereby allowing us to study the nature of relevant promoter species.

Insight into the thermal decomposition of ammonium hexahalogenoiridates(IV) and hexachloroiridate(III).

Thermal decomposition of (NH4)3[IrCl6]·H2O, (NH4)2[IrCl6] and (NH4)2[IrBr6] in reductive and inert atmospheres has been investigated in situ using quick-EXAFS and temperature-resolved powder X-ray diffraction. For the first time, (NH4)2[Ir(NH3)Cl5] and (NH4)2[Ir(NH3)Br5] have been proven as intermediates of thermal decomposition of (NH4)3[IrCl6]·H2O, (NH4)2[IrCl6] and (NH4)2[IrBr6]. Thermal degradation of (NH4)2[IrCl6] and (NH4)2[IrBr6] is a more complex process as suggested previously and includes simultaneous formation of (NH4)2[Ir(NH3)Cl5] and (NH4)2[Ir(NH3)Br5] intermediates mixed with metallic iridium. In the inert atmosphere, complexes (NH4)[Ir(NH3)2Cl4] and (NH4)[Ir(NH3)2Br4] as well as [Ir(NH3)3Br3] were proposed as possible intermediates before formation of metallic iridium particles.

Quick-EXAFS and Raman monitoring of activation, reaction and deactivation of NiCu catalysts obtained from hydrotalcite-like precursors.

The understanding of phase transformation upon activation, reaction and deactivation of catalysts is of prime importance for tailoring catalysts with better performances. Herein we combined Quick-EXAFS and Raman spectroscopies in operando conditions through the monitoring of reaction products by mass spectrometry in order to study in depth active species and deactivating ones for Ethanol Steam Reforming reaction. Quick-EXAFS data analyzed by multivariate analysis allows one to determine the nickel and copper species involved during the activation of a Ni-Cu hydrotalcite-like precursors. Upon reaction and regeneration monitoring, Raman spectroscopy combined with mass spectrometry highlights the side products formed upon ESR leading to the formation of amorphous coke species encapsulating active metallic species and inducing catalyst deactivation. The coke encapsulation of active species was demonstrated by the simultaneous observation of oxidation of nickel and copper as soon as the amorphous coke was burnt by the oxidative regeneration treatment. Formation of filamentous coke species is also confirmed as causing little impact in catalyst deactivation.

Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV-Vis/ATR-IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas-Liquid Phase Reactions.

Operando EPR, XANES/EXAFS, UV-Vis and ATR-IR spectroscopic methods have been coupled for the first time in the same experimental setup for investigation of unclear mechanistic aspects of selective aerobic oxidation of benzyl alcohol by a Cu/TEMPO catalytic system (TEMPO=2,2,6,6-tetramethylpiperidinyloxyl). By multivariate curve resolution with alternating least-squares fitting (MCR-ALS) of simultaneously recorded XAS and UV-Vis data sets, it was found that an initially formed (bpy)(NMI)CuI - complex (bpy=2,2'-bipyridine, NMI=N-methylimidazole ) is converted to two different CuII species, a mononuclear (bpy)(NMI)(CH3 CN)CuII -OOH species detectable by EPR and ESI-MS, and an EPR-silent dinuclear (CH3 CN)(bpy)(NMI)CuII (µ-OH)2 ⋅CuII (bpy)(NMI) complex. The latter is cleaved in the further course of reaction into (bpy)(NMI)(HOO)CuII -TEMPO monomers that are also EPR-silent due to dipolar interaction with bound TEMPO. Both Cu monomers and the Cu dimer are catalytically active in the initial phase of the reaction, yet the dimer is definitely not a major active species nor a resting state since it is irreversibly cleaved in the course of the reaction while catalytic activity is maintained. Gradual formation of non-reducible CuII leads to slight deactivation at extended reaction times.

In Situ Observation of Atomic Redistribution in Alloying Gold-Silver Nanorods.

The catalytic performance and optical properties of bimetallic nanoparticles critically depend on the atomic distribution of the two metals in the nanoparticles. However, at elevated temperatures, during light-induced heating, or during catalysis, atomic redistribution can occur. Measuring such metal redistribution in situ is challenging, and a single experimental technique does not suffice. Furthermore, the availability of a well-defined nanoparticle system has been an obstacle for a systematic investigation of the key factors governing the atomic redistribution. In this study, we follow metal redistribution in precisely tunable, single-crystalline Au-core, Ag-shell nanorods in situ, both at a single particle and an ensemble-averaged level, by combining in situ transmission electron spectroscopy with in situ extended X-ray absorption fine structure validated by ex situ measurements. We show that the kinetics of atomic redistribution in Au-Ag nanoparticles depend on the metal composition and particle volume, such that a higher Ag content or a larger particle size led to significantly slower metal redistribution. We developed a simple theoretical model based on Fick's first law that can correctly predict the composition- and size-dependent alloying behavior in Au-Ag nanoparticles, as observed experimentally.

An easily accessible Re-based catalyst for the selective conversion of methanol: evidence for an unprecedented active site structure through combined operando techniques.

Heterogeneous Re/SiO(2) catalysts prepared using a one pot sol-gel synthesis were found to display high activity in the direct, selective methanol conversion to methylal, which is correlated to an unprecedented rhenium oxide structure.